Make checkstyle happy (remove unused import)

Author: jann0k

cdoc2-lib/src/main/java/ee/cyber/cdoc2/crypto/keymaterial/encrypt/EncryptionKeyMaterialCollectionBuilder.java

@@ -20,7 +20,6 @@
 import java.util.Collection;
 import java.util.LinkedList;
 import java.util.List;
-import java.util.stream.Collectors;
 
 import static ee.cyber.cdoc2.crypto.KeyLabelTools.createCertKeyLabelParams;
 import static ee.cyber.cdoc2.crypto.KeyLabelTools.createPublicKeyLabelParams;